Resist materials and their use in the lithographic processing of substrates, such as silicon wafers, are well known in the electronics industry. In conventional lithographic processing, a substrate is coated with one or more layers of material, at least one of which is radiation sensitive. The radiation sensitive material is generally organic in nature and is typically polymeric. The structure is pattern irradiated with a source of radiation such as light, electron beam, x-ray, gamma ray and the like. The irradiation alters the solubility of the sensitive layer in a developer solvent, or the resistance thereof to a plasma.
Development of the sensitive layer by a solvent, or plasma, will remove either the irradiated or the nonirradiated portion thereof, thus forming a patterned mask for the lithographic processing, e.g., etching, pattern deposition, ion implantation and the like, of the underlying substrate.
There are a number of disadvantages associated with resist lithography which are likewise well known. These include resolution limitations with certain processing techniques, cost of equipment for techniques such as electron beam or ion beam irradiation, loss of pattern definition due to separation of a portion of the radiation sensitive layer from the substrate during development and/or subsequent processing, and the like. A further problem inherent in conventional lithographic techniques is loss of pattern resolution due to backscattering of the irradiation from the substrate into nonirradiated portions of the resist. This can be particularly troublesome, for example, in patterning of a photoresist over a highly reflective substrate, such as aluminum. In addition to backscattering, irradiation with an electron beam can produce a charge build-up in the resist layer which can cause aiming errors and pattern misalignment. These problems are conventionally addressed by adding additional layers of material to the resist structure to absorb backscattering radiation or dissipate charge build-up.
There is an ongoing search for new resist materials, or materials which can be incorporated into conventional resist structures, which will provide improvement in one of these problem areas, e.g., improved adhesion to the substrate or greater contrast, i.e., differential solubility or etchability of the irradiated vs. the nonirradiated portion of the resist layer, without material sacrifice of other desirable properties. There is also considerable interest in new solvents, etch gas mixtures, processing conditions and the like which will improve known resist materials.
In accordance with this invention, a lithographic process is provided which does not require an irradiation step and which is applicable to polymeric materials not presently regarded as useful in lithographic processing.